In binary-cycle plants the cycle efficiency improves as pumping energy is reduced and from maximizing the enthalpy gain of the working fluid for a given amount of heat extracted from the geothermal source brine. Enthalpy gain of the working fluid in the heat exchanger occurs principally from sensible heat gained while passing through the heat exchanger in the liquid state and from vaporization of the organic working fluid near the exit of the heat exchanger. Additional heat transfer is limited after the vapor phase transition due the low thermal conductivity and heat capacity of the vapor. Also, operating pressures and temperatures are constrained by the bulk phase behavior and thermodynamic properties of the working fluid (boiling point, latent heat of vaporization, density, heat capacity, etc.). The fundamental underlying goal of this project is to overcome the cycle efficiency limitations imposed by the bulk thermodynamic proper-ties of the working fluid by introducing a metal-organic heat carrier (MOHC) into the system.

Develop a new type of biphasic working fluid for subcritical geothermal systems that utilizes microporous metal-organic solids as the primary heat carrier and heat transfer medium to support an organic Rankine cycle.